1. Field of Art
This disclosure generally relates to the field of nonvolatile memory, particularly nonvolatile memory bitcell layouts.
2. Description of the Related Art
Nonvolatile memory (NVM) refers to memory that persistently stores information bits when not powered. A nonvolatile memory bitcell (NVM bitcell) stores a single bit of data. Some types of NVM bitcells are implemented using transistors with floating gates. The amount of charge residing on a floating gate determines whether the bitcell is storing a logical “1” or a logical “0”. The floating gate is referred to as “floating” because the gate is electrically isolated from the surroundings by an oxide or dielectric. Some NVM can store more than one state in the bitcell.
In order to expand applications and reduce costs of memory devices, it is desirable to accommodate a large number of bitcells in a given area. It is also desirable to decrease the cost of fabricating each bitcell by using standard complementary metal-oxide-semiconductor manufacturing processes (“CMOS processes”). Currently available memory devices include EEPROM and eFLASH, both of which have disadvantages. Currently, eFLASH has a very small bitcell, but requires steps in addition to the standard CMOS process, which increases the cost of producing the bitcell and possibly changes the performance or characteristics of the produced devices. EEPROM is compatible with standard CMOS processes, but has a relatively large bitcell size, and thus is only suitable for low bit count memories.